Publication Info.

Transactions of the Korean Society of Mechanical Engineers A
(대한기계학회논문집A)

Aim & Scope

The Transactions of the Korean Society of Mechanical Engineers "A" is a monthly periodical published on the 1st day of each month. The aim of the journal is to provide an international forum for the publication and dissemination of original works that contribute to the understanding of the following fields of mechanical engineering: Materials and Fracture, CAE (Computer-Aided Engineering) and Applied Mechanics, Dynamics and Control, Production and Design Engineering, and Reliability. Manuscripts may fall into several categories including regular contributed papers, technical papers, solicited/unsolicited reviews or commentaries.

Volume 27
Issue 9

Most optimization problems do not consider tolerance of design variables and design parameters. Ignorance of these tolerances may not fit for the practical problems and can lead to an unexpected conclusion. That is why we suggest robust optimization considering tolerances in both design variables and problem parameters. Using robust optimization, we designed minimum weight annular finned heat transfer tube subject to constraints on limitation of pressure difference and minimum value of total heat transfer. Consequently, robust optimization satisfies tolerance considered practical problems.

The fatigue life and tensile strength of JLF-1 steel (Fe-9Cr-2W-V-Ta) and its TIG weldment were investigated at the room temperature and $400^{\circ}C$. Four kinds of test specimens, which associated with the rolling direction and the TIG welding direction were machined. The base metal of JLF-1 steel represented almost anisotropy in the tensile properties for the rolling direction. And the base metal of JLF-1 steel showed lower strength than that of TIG weldment. Also, the strength of all materials entirely decreased in accordance with elevating test temperature. Moreover, the fatigue limit of weld metal was largely increase than that of base metal at both temperatures. The fatigue limit of JLF-1 steel decreased in accordance with elevating test temperature. The fatigue limit of JLF-1 steel decreased in accordance with elevating test temperature. The SEM fractography of tensile test specimen showed conspicuous cleavage fracture of a radial shape. In case of fatigue life test specimen, there were so many striations at crack initiation region, and dimple was observed at final fracture region as a ductile fracture mode.

In code roll forming processes, the sheet metal strip is gradually and successively bent into a desired profile. Occurrence of buckling is one of the major defects. Buckling may occur due to longitudinal stress and it is difficult to predict buckling behavior. In this study an analytical method for buckling behavior during roll forming is proposed. All numerical simulations are performed by finite element analysis. The behavior of buckling can be predicted with the simulation modeling of the finite element method.

The problem of reducing the level of vibrations in structures arises in various branches of technology. For the calculation of systems equipped with DVAs, the frequencies of the protected system's free vibrations are determined first. In most practical problems system have to be considered continuous systems. It is important to obtain the detailed information about not the first frequency and the mode but anothers corresponding to it. So, this paper describes the method to obtain the accurate information about the combined discrete system. This information is obtained from the combined system's receptance. This paper shows the convenience when design the dynamic vibration absorber with the combined system's receptance.

This paper presented the real-time self-tuning learning control based on evolutionary computation, which proves its superiority in finding of the optimal solution at the off-line learning method. The individuals of the populations are reduced in order to learn the evolutionary strategy in real-time, and new method that guarantee the convergence of evolutionary mutations is proposed. It is possible to control the control object slightly varied as time changes. As the state value of the control object is generated, evolutionary strategy is applied each sampling time because the learning process of an estimation, selection, mutation is done in real-time. These algorithms can be applied; the people who do not have knowledge about the technical tuning of dynamic systems could design the controller or problems in which the characteristics of the system dynamics are slightly varied as time changes.

This paper provides plastic limit load solutions of cylinders with circumferential part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic-perfectly-plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both external and internal cracks are considered. Furthermore, in terms of the crack shape, both semi-elliptical and constant-depth surface cracks are considered. The resulting limit load solutions are given in a closed form, and thus can be easily used in practical situations. Being based on detailed 3-D FE limit analysis, the present solutions are believed to most reliable, and thus to be valuable information for integrity assessment of piping.

The displacement vector field can be represented in terms of a scalar potential ${\phi}$ and a vector potential ${\phi}$. The scalar potential ${\phi}$ is related to dilatational waves and the vector potential ${\phi}$ is related to rotational waves. Using these two complex displacement potentials, the stress and displacement fields for steadily growing interface cracks in dissimilar materials are obtained. The energy release rate for steadily growing interface cracks in dissimilar materials are also obtained. And with photoelastic isochromatic patterns simulated by computer graphics, the stress intensity factors are discussed.

A modeling method for the modal analysis of a composite trapezoidal plate undergoing in-plane translational acceleration is presented in this paper. The equations of motion for the plate are derived and transformed into a dimensionless form. The effects of the inclination angles, fiber orientation angle and the acceleration on the modal characteristics of the plate are investigated.

This study proposes a new conceptual Hybrid Electric Brake System (HEBS) which overcomes problems of a conventional hydraulic brake system. HEBS adopt a contactless type bake system when a vehicle speed is high, to obtain superior braking performances by eddy current. On the contrary, when a vehicle speed is low, HEBS employs a contact type brake system such as conventional hydraulic brake system to generate higher brake force. Therefore, HEBS transfers faster the braking intention of drivers and guarantees the safety of drivers. Braking torque analysis is performed by using a mathematical model which is proposed to investigate the characteristic of a vehicle dynamics when the brake torque is applied. Optimal torque control is achieved by maintaining a desired slip corresponding to the road condition. The results show that HEBS reduces the stopping distance, saves the electric energy, and increases the stability.

Physical importance of cutting temperatures has long been recognized. Cutting temperatures have strongly influenced both the tool life and the metallurgical state of machined surfaces. Temperatures in drilling processes are particularly important, because chips remain in contact with the tool for a relatively long time in a hole. Tool temperatures tend to be higher in drilling processes than in other in machining processes. This paper concerns with modeling of thermal behaviors in drilling processes as well as estimation of the cutting temperature distribution based on remote temperature measurements. One- and two-dimensional estimation problems are proposed to analyze drilling temperatures. The proposed thermal models are compared with solutions of finite element methods. Observer algorithms are developed to solve inverse heat conduction problems. In order to apply the estimation of cutting temperatures, approximation methods are proposed by using the solution of the finite element method. In two-dimensional analysis, a moving heat source according to feedrate of the drilling process is regarded as a fixed heat source with respect to the drilling location. Simulation results confirm the application of the proposed methods.

In numerical analysis for hydroforming process, the stress calculation is effected by flow stress which is general obtained by stress-strain relationship from uni-axial tension test, so the result of the analysis, especially in tube hydroforming, has limitation of accuracy, tubes are made in roll-forming process and become work-hardened. Then roll forming process causes material properties between rolling direction and circumstantial direction of the tube to be different. So it is difficult to predict material behavior in the process condition of bi-axial stress state. In this study, the flow stress of the tube is determined by inverse engineering approach and bulge test that is widely used for formability test in the condition of bi-axial stress. And Hill's quadratic yield function and flow rule are used to consider the anisotropy of the tube in the roll forming process.

Deep X-ray lithography (DXRL), a fabrication method for the production of microstructures with a high aspect ratio, plays an important role in the subsequent electroplanting process. However, secondary radiation is generated during X-ray exposure and damages the resist adhesion to the metal layer. To solve adhesion problems, we modified the conventional DXRL process, changing the sequence of polymer adhesion in DXRL process. With optimized X-ray exposure and development conditions based on a calculated and modified X-ray power spectrum, we fabricated various polymer microstructures and achieved a maximum aspect ratio of 40.

Translucent plastics are commonly used in packaging of mechanical and/or electrical components. Although Rapid Prototyping(RP) provides prototypes of various materials, translucent RP parts are not readily available from most RP processes. ABSi is one of the ABS materials available for Stratasys' FDM process, and the material had potential to be translucent. In this paper, two post-processing techniques were applied in order to increase optical transmissivity of the parts made of FDM's ABSi. First, elevated temperature condition was applied resulting in increased transmissivity while dimensional shrinkage was observed. Second, resin infiltration and surface sanding provided up tp 16 ％ transmissivity without shrinkage. These post-processes can be selectively applied to increase transmissivity of ABSi parts. Thus, translucent FDM part can be fabricated from regular FDM process followed by the post-processes developed in this study.

This paper compiles solutions of plastic $\eta$ factors and crack tip stress triaxialites for standard and nonstandard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament-to-thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental J estimation than that of the LLD, for all cases considered in the present work. Moreover, the J estimation based on the load-CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing specimen with any thickness. The effects of in-plane and out-of-plane constraint on the crack tip stress triaxiality are also quantified, so that when experimental J value is estimated according to the procedure recommended in this paper, the corresponding crack tip stress triaxiality can be estimated. Moreover, it is found that the out-of-plane constraint effect is related to the in-plane constraint effect.

A lot of researches have been performed on the equal channel angular pressing (ECAP) which produces ultra-fine grains. Along with the experiments, the finite element method has been widely employed to investigate the deformation behavior of specimen during ECAP and the effects of process parameters of ECAP. In this paper, pure-Zirconium is considered for ECAP process by using three-dimensional finite element analysis. The results have been compared with those of previous two-dimensional analysis and with the experimental results

Efficient layout in a fixed work volume reduces build time when multiple parts are built at once in stereolithography systems. An efficient algorithm is developed for 3D layout planning. And it reduces build time and increases efficiency of SLA system. Genetic algorithm is implemented to locate as many parts as possible in the fixed work volume. A 3D collision detection algorithm, k-DOPs Tree, is implemented for the fast evaluation of a layout plan.

Finite element analysis using modern constitutive equation is one of the most general tools to simulate the deformation behavior and to predict the life of the structure. Constitutive equation becomes complicated so as to predict the material behavior more accurately than the classical models. Because of the complexity of constitutive model, numerical treatment becomes so difficult that the calculation should be verified carefully. One-element tests, simple tension or simple shear, are usually used to verify the accuracy of finite element analysis using complicated constitutive model. Since this test is mainly focused on the time integration scheme, it is also necessary to verify the equilibrium iteration using material stiffness matrix and to compare FE results with solution of structures. In this investigation, viscoplastic solution of thick walled cylinder was derived considering axial constraints and was compared with the finite element analysis. All the numerical solutions showed a good coincidence with FE results. This numerical solution can be used as a verification tool for newly developed FE code with complicated constitutive model.

The prediction of the inelastic behavior of the structure is an essential part of reliability assessment procedure, because most of the failures are induced by the inelastic deformation, such as creep and plastic deformation. During decades, there has been much progress in understanding of the inelastic behavior of the materials and a lot of inelastic constitutive equations have been developed. The complexity of these constitutive equations generally requires a stable and accurate numerical method. The radial return mapping is one of the most robust integration scheme currently used. Nonlinear kinematic hardening model of Armstrong-Fredrick type has recovery term and the direction of kinematic hardening increment is not parallel to that of plastic strain increment. In this case, The conventional radial return mapping method cannot be applied directly. In this investigation, we expanded the radial return mapping method to consider the nonlinear kinematic hardening model and implemented this integration scheme into ABAQUS by means of UMAT subroutine. The solution of the non-linear system of algebraic equations arising from time discretization with the generalized midpoint rule is determined using Newton method and bisection method. Using dynamic yield condition derived from linearization of flow rule, the integration scheme for elastoplastic and viscoplastic constitutive model was unified. Several numerical examples are considered to demonstrate the efficiency and applicability of the present method.

This paper proposes a robust method for the Ramberg-Osgood(R-O)fit to accurately estimate elastic-plastic J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover, for practical applications, the method is given not only for the case when full stress-strain data are available but also for the case when only yield and tensile strengths are available. Reliability of the proposed method for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels. Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J results based on deformation plasticity using various R-O fits are compared with reference J values. Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed, together with its accuracy.

In this paper, the finite element equations for the transient linear viscoelastic stress analysis are presented in time domain, whose variational formulation is derived by using the Galerkin's method based on the equations of motion in time integral. Since the inertia terms are not included in the variational formulation, the time integration schemes such as the Newmark's method widely used in the classical dynamic analysis based on the equations of motion in time differential are not required in the development of that formulation, resulting in a computationally simple and stable numerical algorithm. The viscoelastic material is assumed to behave as a standard linear solid in shear and an elastic solid in dilatation. To show the validity of the presented method, two numerical examples are solved nuder plane strain and plane stress conditions and good results are obtained.

In this paper, we performed the improvement study for the dynamic characteristics enhancement of the motor stator coil vertical winding machine. The dynamic characteristics improvement was done by means of the optimized design and the weight reduction of the flyer configuration, modified design of the servo control system for the flyer and the former actuation, and the development of jump timing digital circuit for the reduction of former jumping error. As the results, the maximum winding speed pattern of the developed machine was attained up to 3000rpm and also reduced the jumping error. In conclusion, domestic design technology for manufacturing the motor coil vertical winding machine was established through this study.

Static analysis using hybrid finite element(FE) method has been applied to characterize the influence of position, runout and thickness errors of the sun, ring and planet on the bearing forces and critical tooth stress. Some guidelines for tolerance control to manage critical stress and bearing forces are deduced from the results. Carrier indexing error planet assembly and planet tooth thickness error are most critical to reduce planet bearing force and maximize load sharing as well as to reduce critical stresses. Sun and carrier bearing forces due to errors increase several times more than those of normal condition.

An experimental method to measure Q-parameter in-situ is described. The basic idea comes from the fact that the side necking near a crack tip indicates the loss of stress triaxiality, which can be scaled by Q. From the out-of-plane displacement and the in-plane strain near the surface of side necking, stress field averaged through the thickness is calculated and then Q is determined from the difference between the stress field and the HRR field corresponding to the identical J-integral. To prove the validity, three-dimensional finite element analysis has been performed for a CT configuration with side-groove. Q-value which was calculated directly from the near-tip stress field is compared with that determined by simulating the experimental procedure according to the proposed method, that is, the Q-value determined from the lateral displacement and the in-plane strain. In addition, the effect of location where the displacement and strain are measured is explored.